Fairchild F8

processor An 8-bit microprocessor. The processor itself

had no address bus - program and data memory access were

contained in separate units, which reduced the number of pins

and the associated cost. It also featured 64 registers,

accessed by the ISAR register in cells (register windows) of

eight, which meant external RAM wasn't always needed for

small applications. In addition, the 2-chip processor didn't

need support chips, unlike others which needed seven or more.

The F8 inspired other similar CPUs, such as the Intel8048. The use of the ISAR register allowed a subroutine to

be entered without saving a bunch of registers, speeding

execution - the ISAR would just be changed. Special purpose

registers were stored in the second cell (regs 9-15), and the

first eight registers were accessed directly. The windowing

concept was useful, but only the register pointed to by the

ISAR could be accessed - to access other registers the ISAR

was incremented or decremented through the window.

(1994-11-16)